1. Field of the Invention
The present invention relates to radio communication systems, radio communication methods, and base stations, and more particularly, to a radio communication system, a radio communication method, and a small-area base station, such as a femtocell base station, which achieve a reduction in power usage and a reduction in interference.
2. Description of the Related Art
In conventional mobile communication systems, base stations (BSs) are radio communication equipments that provide connections in order to communicate with mobile stations (MSs). Most of them are large-area radio base stations called macrocell base stations having cell radii of about several hundred meters to several tens of kilometers.
In recent years, smartphones and tablet PCs have been widely used, and data communication has been rapidly increased. As a result, the load on macrocell base stations have been rapidly increased. In order to cope with this heavy traffic, many new off-loading technologies have been researched that makes communication quality stable by transferring the traffic to other communication systems. One idea of the technology is femtocell base stations. Femtocell base stations are one type of base stations used in radio communication systems and are small-area base stations having cell radii of about as small as several meters to as large as several tens of meters. Femtocell base stations can provide communication services through broadband lines already installed, such as asymmetric digital subscriber lines (ADSLs), coaxial cables, and optical fiber. Therefore, femtocell base stations allow data traffic to be off-loaded and can also cover the cell areas in indoor facilities which radio waves do not reach easily, such as houses and offices, while keeping the mobility of mobile stations. Since these femtocell base stations are installed directly by users in houses and offices, communication providers can reduce the operation cost. When communication providers use such femtocell base stations effectively to improve the communication quality of cell areas where existing macrocell base stations cannot cover, the communication providers provide better communication services for the communication subscribers.
These femtocell base stations can be roughly divided into three types, open access, closed access, and hybrid access modes. Open-access-mode femtocell base stations allow any mobile stations to use communication services freely without prior registration. Closed-access-mode femtocell base stations provide communication services only for mobile stations registered in advance. Hybrid-access-mode femtocell base stations apply different qualities of service (QoS) to mobile stations registered in advance and mobile stations without prior registration. These types of femtocell base stations can be implemented with the use of the high rate packet data (HRPD) technology using cdma 2000, described in C. S0024 cdma 2000 High Rate Packet Data Air Interface Specification by the third generation partnership project 2 (3GPP2).